Core/Spells: implement DoT clipping

* Core/Spells: Implementation of DoT clipping.
* Core/Utilities: Backport "EnumFlags v3.0" from master.
* Core/Spells: Switch AURA_REMOVE_MODE to a flag set.

src/server/scripts/Spells/spell_quest.cpp

@@ -2544,7 +2544,7 @@ class spell_q10929_fumping : SpellScriptLoader
 
             void HandleEffectRemove(AuraEffect const* /*aurEff*/, AuraEffectHandleModes /*mode*/)
             {
-                if (GetTargetApplication()->GetRemoveMode() != AURA_REMOVE_BY_EXPIRE)
+                if (!GetTargetApplication()->GetRemoveMode().HasFlag(AuraRemoveFlags::Expired))
                     return;
 
                 if (Unit* caster = GetCaster())